1. Field of the Invention
The present invention relates to multicomponent optical devices and, more particularly, to various arrangements including regions with different optical properties such that a single device may perform a number of different optical functions. A manufacturing technique related to batch fabrication of such devices is also disclosed.
2. Description of the Prior Art
Many optical communication systems require various passive optical components such as, for example, lenses, optical isolators, dichroic filters, and polarization splitters. Lenses are used to couple light between active devices (e.g., lasers or LEDs) and optical fibers. These lenses have many different geometries, as indicated by the common use of spherical lenses and cylindrical graded index lenses. Optical isolators may be used in applications such as high bit rate transmitters and optical amplifiers to prevent reflected signals from re-entering active semiconductor optical devices such as lasers. Dichroic filters are often utilized in multiplexer/demultiplexer schemes to separate the various operating wavelengths and to increase the capacity of the communication system. Polarization beam splitters are used in coherent optical receivers which require polarization diversity to achieve data recovery. Many requirements for other passive optical components also exist.
Additionally, the packaging assembly processes for many lightwave devices include many time-consuming and expensive operations. For example, in most conventional lightwave communication systems, the multiplicity of passive optical components are individually mounted and aligned. The alignment operation becomes problematic in packages of relatively small size which necessitates extremely tight spaces between components. The reduction in package size additionally increases the need to reduce, where possible, the number of such components contained in a single package. Mechanical stability of the final package is another demand on the system design.
There exist in the optics art various spherical couplers which include a first spherical lens embedded within a second coupling component. U.S. Pat. No. 4,257,672 issued to L. Balliet on Mar. 24, 1981 discloses one such arrangement with a spherical core lens completely surrounded by a spherical shell. The index of refraction of the core is greater than that of the shell. The Balliet sphere is utilized to provide coupling between an LED and an optical fiber. In an alternative arrangement disclosed in U.S. Pat. No. 4,557,566 issued to K. Kikuchi et al. on Dec. 10, 1985, a spherical core is surrounded by a cladding which is half spherical and half cylindrical, forming a GRIN-spherical confocal lensing arrangement. These and other prior art designs are deemed to be relatively simple arrangements which may perform only the function of coupling the optical signal between an active optical device (e.g., laser, LED) and the transmitting fiber.
U.S. Pat. No. 4,753,489 issued to W. F. M. Tolksdorf et al. on Apr. 5, 1988 discloses an alternative spherical device particularly developed for rotating the plane of polarization of linearly polarized light passing therethrough. In particular, the Tolksdorf et al. device comprises a ball lens made from magnetic crystalline material preferentially magnetized in the direction of light transmission, where the ball lens consists of two domes of magnetic garnet material whose basal planes are oriented parallel to one another and perpendicular to the direction of light transmission, with a spherical member between the domes consisting of optically transparent non-magnetic garnet material. The sphere can be rotated to adjust the effective thickness of the magnetic material, thus providing the ability to match the magnetooptical rotation to the wavelength of the light signal propagating therethrough. In fabrication, equally thick layers of magnetic garnet material are epitaxially deposited on the major surfaces of a substrate consisting of optically transparent non-magnetic garnet material. The coated substrate is then sawed into cubes, and the cubes are ground to form spheres. The Tolksdorf et al. process is considered to contain several drawbacks. For example, there is considerable difficulty in growing epitaxial layers on opposite major surfaces of a substrate such that the epitaxial layers are equally thick. Additionally, epitaxial growth is known to be a thickness-limited process, due to slow growth rates and relatively large strains from mismatched lattice sizes. Therefore, the ability to form spherical polarization rotators of the relatively large size (as compared to integrated circuits utilizing epitaxial growth techniques) required for most optical applications is questionable in the Tolksdorf et al. process. Further, the type of optical device which may be fabricated is limited to those which require only the epitaxial deposition of similar materials. Additionally, the actual device structure as disclosed by Tolksdorf et al. may suffer performance limitations in that the magnetic material performing the desired rotation is formed in a manner such that the magnetic material performing the desired rotation is formed in a manner such that the magnetic domes are not uniformly thick. Therefore, a linearly polarized signal passing through the central axis (indicated by numeral 9 in the figure), where the dome thickness is maximum, would experience a greater rotation than those signals traveling in parallel paths, displaced from axis 9 where the dome thickness is smaller. Lastly, the device as disclosed by Tolksdorf et al. requred additional discrete, external components (i.e., polarizers) in order to perform the complete optical isolation function.
In light of the above, therefore, a need remains in the prior art for a means of reducing the size, cost, alignment difficulties, fabrication problems and various other limitations in lightwave communication arrangements which require a number of separate optical functions.